The present invention relates to generally fluorescent lamps whose inside surface is coated with fluorescent materials and which are filled with mercury vapor and rare gas and more particularly U-shaped fluorescent lamps which are extremely compact in size.
Of all the light sources the incandescent lamps have the highest degrees of freedom in design. In other words they are superior in compactness to other light sources. As a result they have been widely used in various fields. However their luminous efficiency and lamp life are about 1/5 of those of the fluorescent lamps so that from the standpoint of efficient use of energy they are disadvantageous.
The fluorescent lamps may be divided in general into the straight and circular types, but both the types are not so compact as to be used instead of the incandescent lamps.